The invention relates to a device for removing moisture from materials in the form of individual sheets carrying a photographic layer. The device is equipped with a pair of transport rollers at the incoming side and another pair of transport rollers on the exit side.
Carrier materials in sheet form for photographic layers, such as for example individual sheets of exposed photographic paper, are customarily developed only in so-called minilabs. In large laboratories, on the other hand, the individual pictures are exposed onto long strips of paper that are cut into individual sheets only after they have been developed and dried. The long paper strips can be processed with significantly simpler means than the individual sheets. Also, long paper strips allow higher throughput speeds. The reason for the lower complexity and higher speed lies in the fact that long paper strips can be processed practically without any threading-in operations. It is normal practice to glue the end of one paper strip to the beginning of the next strip. If the machine is turned off for cleaning or servicing, a leader strip is placed in the machine as a means for pulling the beginning of a new photographic paper strip through the machine when the latter is started up again.
In the processing of individual sheets, on the other hand, the front edge of each sheet has to be threaded into each processing device or each pair of transport rollers along the processing path through the machine. This also applies to devices for removing moisture from the photographic materials between the individual wet-processing stages and before the drier.
Under the existing state of the art, the moisture removal in machines for developing individual sheetsxe2x80x94in contrast to machines for developing strip material in large laboratoriesxe2x80x94has therefore been performed exclusively by means of squeeze-out rollers as described also in the published German patent application DE 41 41 192 A1. In order to improve the poor moisture-removing performance of the squeeze-out rollers, the aforementioned publication proposes the concept of using a combination of several pairs of squeeze-out rollers after each processing bath, so that each sheet runs through at least two pairs of squeeze-out rollers. It was found, however, that even with three pairs of squeeze-out rollers, a very large amount of processing fluid is taken along from one processing tank to the next by the sheets of photographic material. Increasing the number of squeeze-out rollers even further is not considered to be feasible in view of the additional cost and the space required.
The present invention therefore has the object of proposing a device for removing moisture from photographic materials that are processed in the form of individual sheets, so that the device fits into a compact space and ensures a good moisture-removal rate.
A moisture-removing device according to the invention is equipped with a first pair of transport rollers at the incoming side and a second pair of transport rollers at the exit side. A stationary squeeze-out surface and an elastic wiper blade set against the squeeze-out surface are arranged in the path between the first roller pair and the second roller pair. Using a wiper blade in connection with a squeeze-out surface placed in the path between two transport roller pairs strongly improves the effectiveness of the moisture removal in particular for small sheet formats. As a result, a much smaller part of the processing fluid adhering to the photographic sheets is taken along from one processing bath to the next. This offers the benefit that the individual processing baths need to be refreshed less often. At the same time, a higher image quality can be achieved, for example by avoiding traces caused by developer fluid running down the surfaces of the photographs.
It is advantageous if the squeeze-out surface has a low coefficient of friction to prevent the leading edges or the leading portions of the photographic sheets from adhering to the squeeze-out surface. A sheet clinging to the squeeze-out surface would cause a paper jam, which could destroy the affected sheet or would at least necessitate a manual intervention to correct the malfunction.
To avoid the possibility of a paper jam with an even higher degree of assurance, the squeeze-out surface is inclined at an angle between 5xc2x0 and 15xc2x0 in relation to the plane of the transport path of the photographic sheets. Positioning the squeeze-out surface at an angle within this range ensures a safe entry of the leading edges of the sheets between the wiper blade and the squeeze-out surface without blocking the advancement of the leading edge. Also, inclining the squeeze-out surface at an angle within the proposed range prevents that a surface portion of the sheet could cling to the squeeze-out surface.
Photographic paper that has already been transported through a processing tank has a low degree of stiffness. If the leading edge of an individual sheet being advanced by the first pair of transport rollers meets with an obstacle, as represented by the wiper blade and the squeeze-out surface, the sheet can easily be curled into a loop, which will lead to a malfunction. Since the stiffness of the paper decreases progressively the more the leading edge projects from the gap of the first roller pair, the distance of the wiper blade from the first roller pair has to be carefully matched to the contact pressure of the wiper blade against the squeeze-out surface. Good results in the removal of moisture were found to be achievable if the contact pressure of the wiper blade is set so that a photographic sheet can be pulled through the gap between the wiper blade and the squeeze-out surface by applying a width-related pulling force between 5 Newton and 30 Newton per meter of paper width. With a contact pressure determined in this manner, the distance between the first roller pair and the wiper blade should not exceed 40 millimeters.
To ensure an adequate useful operating life of the wiper blade without having to accept scratches on the image surface, blades with a Shore hardness of up to 90xc2x0 have been proven to work well.
The useful operating life of the wiper blades can be improved enormously by taking measures to ensure that the sharp lateral edges of the photographic sheets are not constantly passing the same places on the wiper blades. It is therefore proposed according to the invention to transport the individual sheets through the developing apparatus so that they follow each other in laterally staggered positions rather than in a straight line. It is advantageous to individually determine the lateral offset of each photographic sheet in relation to the immediately preceding sheet, for example by means of a random number generator.
The novel features that are considered as characteristic of the invention are set forth in particular in the appended claims. The improved moisture-removing device itself, however, both as to its construction and its mode of operation, together with additional features and advantages thereof, will be best understood from the following detailed description of a presently preferred specific embodiment with reference to the accompanying drawing.